The present invention relates to a method of and a device for monitoring the function of a safety shut off device in the form of an electromagnetic fuel shut off valve (ELAB) in internal combustion engines, particularly in Diesel engines having an electrical power source, a driving switch, a fuel quantity adjustor acted upon by an electronic Diesel regulating and controlling device (EDC). The invention relates also to a device for carrying out the method.
In a known fuel injection pump for Diesel engines according to German publication DE-OS 2,945,484, a piston arranged in the housing of a fuel injection pump is brought into a reciprocating movement and simultaneously into a rotary movement whereby fuel flows from a suction chamber formed within the pump housing toward the pump piston. From the injection pump, the adjusted quantity of fuel is supplied into pressure conduits leading to cylinders of the Diesel engine. In a connection conduit between the suction chamber and an intake of the pump piston, a safety valve is provided which interrupts the fuel flow from the suction chamber when certain predetermined safety limit conditions are exceeded. For example, a safety limit condition is exceeded when a control lever is adjusted by the gas pedal into its idling position and the delivery pressure in the housing of the fuel injection pump corresponds to a higher rotary speed than that required for an idling operation.
Another known emergency control device for a fuel metering system for use in Diesel engines (DE-OS 3,238,191) includes an emergency control branch which is manually or automatically connectable parallel to a signal processing device having a regulating device for the fuel supply. The emergency control branch is provided with a load pressure regulator and its output signal in the event of an interference is applied by an interference detecting circuit to an adjusting mechanism which delivers to the internal combustion engine the requisite quantity of fuel depending on the mode of operation. To take into account further operational conditions, a minimum value selection circuit can be provided in the emergency control branch.
From the DE-S 1,962,570 a resetting device for a fuel quantity determining member of a fuel injection system of a Diesel engine is known, which becomes activated when an error condition occurs, for example when the regulating circuit itself or a connection to corresponding sensors is interrupted. As a consequence, in the event of a failure the fuel quantity determining member is adjusted for the delivery of small quantities of fuel to be injected. In this known solution where the fuel quantity is metered toward small values, the power output of the internal combustion engine can be reduced to such an extent that, for example during operation in a difficult terrain, the running of the engine can no longer be sustained.
Generally known are also electronic adjusting circuits for regulating the operation of self-igniting internal combustion engines, i.e. Diesel engines. For example, according to DE-OS 3,531,198 an electric adjusting device controlled by electrical signals is known whereby instead of mechanical fuel measuring and regulating systems a central control apparatus (SG) generates the requisite adjusting signals. It is true that mechanical fuel metering systems in Diesel engines are reliable with regard to their safety against errors, nevertheless under circumstances they increasingly fail to be compatible with the requirement to take into account a large number of different operational and environmental conditions.
The application of electronic components in connection with an electronic Diesel regulation (EDC) makes it desirable to employ comprehensive safety, monitoring and emergency measures inasmuch as the individual structural groups by themselves offer the possibility to recognize an error or to eliminate the error.
From DE-OS 3,301,742 it is known to provide a safety device for a self-igniting internal combustion engine with means for the continuous generation of signals corresponding to operational variables of the engine such as gas pedal position, computed desired value of a control rod travel, rotary speed, brake pedal position and the like and to determine by means of a minimum value selection a corrected desired value of the control rod displacement and apply the same to the setting regulator of the controlling device (EDC). This corrected desired value of the control rod displacement serves simultaneously for the determination of a deviation of the regulation from the sensed actual value of the control rod displacement. Upon exceeding predetermined limits the known safety device then reacts either by inactivating the fuel injection pump, deenergizing the end stage or the setting regulator or by introducing an emergency mode of operation. However, with this known safety device problems may occur under certain circumstances inasmuch as all possible marginal conditions are not considered during the determination of the safety conditions. For instance, by the provision of an idle speed contact on the gas pedal it is possible to obtain an idling indication signal. However, this indication signal is of no effect when the engine is equipped with a driving speed regulator, for example. Moreover, it is conceivable that during sport driving, or in order to warn tailgating drivers at high driving speeds, and the like, a driver may for a short time activate or just touch the brake pedal while the gas pedal remains depressed or is not yet in its idling position.
Considering the importance of an electromagnetic shut off valve (ELAB) which acts as a redundant safety shut off member in internal combustion engines to shut off the engine in the case of interference by interrupting the fuel supply, it is desirable to continuously monitor the correct functioning of the electromagnetic shut off valve.
Under normal operational conditions the electronic Diesel regulating and control device (EDC) is capable of detecting a defect in the fuel quantity adjusting mechanism substantially on the basis of a lasting regulating deviation in the adjustment regulating circuit. The controlling device (EDC) then activates via a suitable safety logic circuit the electromagnetic shut off valve to interrupt the fuel supply. Accordingly, the electromagnetic shut off valve (ELAB) acts as a safety member which is able to guarantee a shut off of the engine also in the case of a jammed fuel quantity adjusting mechanism or a short circuited end stage in the EDC-control device, for example. Hence, due to the importance of the shut off safety valve (ELAB) a continuous monitoring of its function is unconditionally necessary. Due to the fact that the fuel shut off safety valve (ELAB) itself is a component part of the fuel metering device similarly as all other components of the system and therefore cannot be tested separately as to its function, difficulties are encountered when it is desirable to continuously test its function because its proper functioning causes the stoppage of the engine. Therefore, the requirement or the possibility to test the operability of the ELAB valve in predetermined time intervals during normal operation of the vehicle cannot be met because of driving safety, inasmuch as the testing would cause a temporary stoppage of the engine.
In addition, a defect in the ELAB valve cannot be recognized by the operator because during the switch off of the power supply the defective ELAB is deenergized and of course power for the fuel quantity adjusting mechanism and other components is also disconnected. Moreover, it cannot be assumed that the driver or the user of the vehicle which is equipped with such a monitoring system would continuously keep in mind or be willing to test a specific safety components in the fuel regulating system of his or her vehicle.